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    Ho 249
    From: Jeremy C
    Date: 2011 Jan 16, 07:06 EST
    There is a big difference between HO 249 and HO 214 or HO 229, and that is the limited declination range of Volume 2 and 3, and very limited number of stars available in Volume 1.
     
    As I see it, HO 249 intends the navigator to use Volume 2 or 3 (depending on Latitude) for your sun, moon, and planet sights and then use Volume 1 (selected Stars) for any star observations.  The main reason that the volumes are smaller is that they have only 29 degrees of declination included instead of the full 90 degrees.  Sadly this limitation eliminates 28 of the main navigational stars, many of which are nice to use in the lower to mid-latitudes, unless they are included in the pre-determined selected stars for your latitude and LHA of Aries in Volume 1.
     
    Of course in this day in age with the computers and calculators this isn't much of an issue, but if you like your tables and see a star poking through the clouds and it's outside of the range of HO 249, you are out of luck.  This won't happen with HO 229 since it's good for the full range of celestial triangles.
     
    HO 229 can also be used for great circle sailings and star identification.  HO 249 can do GC sailings as well, but only if you aren't sailing above 29 degrees of Latitude.  Star ID is also limited by declination.
     
    In the end you are trading weight and bulk for versatility and accuracy, and people should understand this when they choose what book to use.
     
    Jeremy
     
    In a message dated 1/16/2011 6:43:58 A.M. Central Asia Standard Time, glapook---.net writes:
    H.O. 229 takes up a lot of space and is heavy and provides more precision than is actually needed for small craft navigation. H.O. 249, Sight Reduction Tables for Air Navigation,  is much more compact and the arrangement of the tables is more convenient. Both tables are used the same way (with the exception of the second differences correction for slightly greater accuracy for high altitude sights in H.O. 229 that you can skip if you choose) so if you can work one set of tables you can work the other. I suggest you download H.O. 249 from this site:


    http://msi.nga.mil/NGAPortal/MSI.portal

    (click on "Publications")

    print out a few pages and compare with your H.O. 229.

    You can check your work by having the Navy do the computations here:

    http://www.usno.navy.mil/USNO/astronomical-applications/data-services/cel-nav-data

    Since you are just getting started, and before you head gets polluted with these other complicated methods, I suggest you try the flat Bygrave slide rule which you can make for yourself at a cost of a few dollars with the printouts available here:

    https://sites.google.com/site/fredienoonan/other-flight-navigation-information/modern-bygrave-slide-rule

    https://sites.google.com/site/fredienoonan/other-flight-navigation-information/self-contained-long-term-celestial-navigation-system

    The Bygrave computes everything your need in less than two minutes and uses no batteries.

    gl

    --- On Sat, 1/15/11, Patrick Goold <goold{at}vwc.edu> wrote:

    From: Patrick Goold <goold{at}vwc.edu>
    Subject: [NavList] Re: help with sun sights
    To: NavList@fer3.com
    Date: Saturday, January 15, 2011, 2:15 PM

    Gary,
    I am using HO 229. 

    Patrick


    On Fri, Jan 14, 2011 at 10:22 PM, Gary LaPook <glapook---.net> wrote:

    "I am still unclear how to read the reduction tables. Thanks so much!"

    Which tables are you using?

    gl
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    --
    Dr. Patrick Goold
    Department of Philosophy
    Virginia Wesleyan College
    Norfolk, VA 23502
    757 455 3357

    Charles Olson: "Love the World -- and stay inside it."

       
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